Semiconductor memory device and method for manufacturing the same

ABSTRACT

According to one embodiment, a semiconductor memory device includes a stacked body including a plurality of electrode members and a plurality of insulating members, each of the electrode members and each of the insulating members being stacked alternately in a first direction on the substrate. The semiconductor memory device also includes a memory hole that extends in the stacked body in the first direction and a semiconductor member that is disposed to extend in the memory hole in the first direction. The semiconductor memory device also includes a memory member that is disposed between the semiconductor member and the plurality of electrode members. The plurality of electrode members including a first electrode member and a second electrode member, a thickness of the memory member at the position of the first electrode member being greater than a thickness of the memory member at the position of the second electrode member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/976,930, filed May 1, 2018, which is a divisional of U.S. applicationSer. No. 15/343,591, (now U.S. Pat. No. 9,991,274) filed Nov. 4, 2016,which is a continuation of U.S. application Ser. No. 14/645,682 (nowU.S. Pat. No. 9,508,739), filed Mar. 12, 2015, which is based upon andclaims the benefit of priority from U.S. Provisional Patent Application62/049,226, filed on Sep. 11, 2014; the entire contents of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor memorydevice and a method for manufacturing the same.

BACKGROUND

Recently, there has been a trend toward high integration of asemiconductor memory device and thereby a stacked semiconductor memorydevice has been proposed. In a stacked semiconductor memory device, astacked body in which word lines and interlayer insulating members arestacked alternately and a memory hole that penetrates through thestacked body are formed and a memory member is provided on a sidesurface of the memory hole. The memory member is formed to have a blockinsulating member, a charge storage member, and a tunnel insulatingmember, which are stacked from the outer side in this order. A siliconpillar and an insulation member are provided further on the center axisside from the memory member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a semiconductor memorydevice according to a first embodiment;

FIGS. 2 to 5 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to the firstembodiment;

FIG. 6 is a cross-sectional view illustrating the block insulatingmember and the charge storage member before the oxidation in thesemiconductor memory device according to the first embodiment whenviewed from the upper section;

FIG. 7 is a cross-sectional view illustrating the block insulatingmember, the charge storage member after the oxidation, and the tunnelinsulating member in the semiconductor memory device according to thefirst embodiment when viewed from the upper section;

FIG. 8 is a graph illustrating the member thickness of the tunnelinsulating member that is formed through the oxidation, in which thediameter of the memory hole is shown as the abscissa and the memberthickness of the silicon oxide member is shown as the ordinate;

FIG. 9 is a cross-sectional view taken along line IX-IX shown in FIG. 5;

FIG. 10 is a cross-sectional view taken along line X-X shown in FIG. 5;

FIGS. 11 to 14 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to the firstembodiment;

FIG. 15 is a graph illustrating a threshold voltage window of thesemiconductor memory device according to the first embodiment, in whichthe diameter of the memory hole is shown as the abscissa and thethreshold voltage is shown as the ordinate;

FIG. 16 is a cross-sectional view illustrating the semiconductor memorydevice according to a second embodiment;

FIG. 17 is a cross-sectional view taken along line XVII-XVII shown inFIG. 16;

FIG. 18 is a cross-sectional view taken along line XVIII-XVIII shown inFIG. 16;

FIGS. 19 and 20 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to the secondembodiment;

FIG. 21 is a cross-sectional view illustrating the semiconductor memorydevice according to a third embodiment.

FIG. 22 is a cross-sectional view taken along line XXII-XXII shown inFIG. 21; and

FIG. 23 is a cross-sectional view taken along line XXIII-XXIII shown inFIG. 21.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor memory device includes asubstrate. The semiconductor memory device also includes a stacked bodyincluding a plurality of electrode members and a plurality of insulatingmembers, each of the electrode members and each of the insulatingmembers being stacked alternately in a first direction on the substrate.The semiconductor memory device also includes a memory hole that extendsin the stacked body in the first direction and a semiconductor memberthat is disposed to extend in the memory hole in the first direction.The semiconductor memory device also includes a memory member that isdisposed between the semiconductor member and the plurality of electrodemembers. The plurality of electrode members including a first electrodemember and a second electrode member, a diameter of the memory hole at aposition of the first electrode member being smaller than a diameter ofthe memory hole at a position of the second electrode member, and athickness of the memory member at the position of the first electrodemember being greater than a thickness of the memory member at theposition of the second electrode member.

According to one embodiment, a method for manufacturing a semiconductormemory device includes forming a first electrode member on a flatsurface perpendicular to a first direction, forming a second electrodemember parallel to the first electrode member, forming a memory holethat penetrates the first electrode member and the second electrodemember in the first direction, forming a first insulating member on aside surface of the memory hole, and forming a second insulating memberby oxidizing a surface of the first insulating member.

Hereinafter, embodiments of the invention will be described withreference to the drawings.

First Embodiment

First, a first embodiment is described.

FIG. 1 is a cross-sectional view illustrating a semiconductor memorydevice according to the embodiment.

The semiconductor memory device according to the embodiment is a stackedNAND flash memory.

As illustrated in FIG. 1, a silicon substrate 10 is provided in thesemiconductor memory device 1 according to the embodiment and aninsulating member 11 is provided on the silicon substrate 10.

Hereinafter, an XYZ Cartesian coordinate system is employed in thespecification, for convenience of description. That is, in FIG. 1, twodirections which are parallel to a contact surface between the siliconsubstrate 10 and the insulating member 11 and are orthogonal to eachother correspond to “an X-direction” and a “Y-direction”. In addition,an upward direction perpendicular to the contact surface between thesilicon substrate 10 and the insulating member 11 corresponds to a“Z-direction”. In descriptions below, when “upper section” and “lowersection” are used, in the Z-direction, a portion which is further awayfrom the silicon substrate 10 is referred to as the upper section and aportion which is closer to the silicon substrate 10 is referred to asthe lower section.

A back-gate electrode BG, a stopper member 14, a stacked body 13, aninterlayer insulating member 36, a selection-gate electrode SG, aninterlayer insulating member 37, an interlayer insulating member 38, asource line SL, an interlayer insulating member 39, and a bit line BLare provided alternately on the insulating member 11 of thesemiconductor memory device 1 from the lower section along theZ-direction.

A slit ST for separating word lines WL is formed on the stopper member14 such that the slit ST penetrates through the stacked body 13 in theZ-direction. An insulating member 22 that is made of an insulatingmaterial is provided in the slit ST. The insulating member 22 extends inthe Y-direction.

A memory hole MH is formed on the insulating member 11 such that thememory hole MH penetrates the stacked body from the interlayerinsulating member 37 to the back-gate electrode BG in the Z-direction.Each end of a pair of memory holes MH is connected to a junction portionJP which is provided in the back-gate electrode BG and extends in theX-direction. The pair of memory holes MH and the junction portion JPform a U shape.

A memory member 15 is provided on side surfaces of the pair of memoryholes MH and the junction portion JP. A silicon pillar SP is provided ona side surface of the memory member 15. An insulating member 21 isprovided on the central axis side from the silicon pillar SP. Thesilicon pillar SP has a U shape. A memory cell is formed in a portion ofthe word line WL intersecting with the silicon pillar SP.

A contact plug CP_(SL) that is embedded in the interlayer insulatingmember 38 is provided on one end of the U-shaped silicon pillar SP. Asource line SL that is embedded in the interlayer insulating member 39and extends in the Y-direction is provided on the contact plug CP_(SL).A contact plug CP_(BL) that is embedded in the interlayer insulatingmember 38 and interlayer insulating member 39 is provided on the otherend of the silicon pillar SP. The bit line BL that extends in theX-direction is provided on the contact plug CP_(BL) and the interlayerinsulating member 39.

The memory member 15 is formed to have a block insulating member 27, acharge storage member 26, and a tunnel insulating member 25 which arestacked from the outer side in this order. The block insulating member27 is formed of, for example, silicon oxide (SiO₂). The charge storagemember 26 is formed of, for example, silicon nitride (Si₃N₄). The tunnelinsulating member 25 is formed of silicon oxide obtained by oxidizingthe charge storage member 26 that is formed of silicon nitride.

Normally, the tunnel insulating member 25 has insulation properties buta tunneling current flows through the member when a predeterminedvoltage within a range of drive voltages of the semiconductor memorydevice 1 is applied. In a case where the tunnel insulating member 25 isthin and, for example, the member thickness is 4 nm or less, a directtunneling current flows through the member. The charge storage member 26is capable of storing charge and, for example, is formed of a materialwhich has electron trap sites. Practically, no current flows through theblock insulating member 27 even when a voltage within a range of drivevoltages of the semiconductor memory device 1 is applied.

The thickness of the silicon oxide formed through oxidation variesdepending on a distance from the central axis of the memory hole MH tothe side surface of the charge storage member 26 at the time of formingthe charge storage member 26.

The insulating member 11 and the interlayer insulating members 12 and 36to 39 are formed of, for example, silicon oxide (SiO₂). The back-gateelectrode BG and the word lines WL, and selection-gate electrode SG areformed of, for example, silicon (Si). The stopper member 14 is formedof, for example, a tantalum oxide member (Ta₂O₅). The contact plugCP_(SL), the contact plug CP_(BL), the source line SL, and the bit lineBL are formed of, for example, tungsten (W).

A diameter of the memory hole MH is larger at the upper section and thelower the section, the smaller the diameter. A member thickness of thetunnel insulating member 25 is less at the upper section and the lowerthe section, the greater the thickness.

Hereinafter, a diameter of a circumscribed circle of the memory hole MHin an XY plane is referred to as a diameter of the memory hole MH.

Next, a method for manufacturing the semiconductor memory deviceaccording to the embodiment will be described.

FIGS. 2 to 5 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to theembodiment.

First, as illustrated in FIG. 2, the insulating member 11 that is formedof silicon oxide is formed on the silicon substrate 10 through, forexample, high density plasma chemical vapor deposition (HDP-CVD) and theback-gate electrode BG is formed on the insulating member 11. Then, arange in which a groove 33 is formed using lithography is specified,etching is performed, and thereby the back-gate electrode BG isselectively removed such that the groove 33 is formed. Then, forexample, non-doped silicon is caused to be deposited in the groove 33such that a sacrificial member 34 is formed. Being non-doped indicatesthat impurities (dopant impurities) which impart conductivity to thesilicon are not added intentionally such that no dopant impurities arecontained practically except for elements produced due to a source gasduring the deposition. Then, for example, the tantalum oxide member(Ta₂O₅) is caused to be deposited on the back-gate electrode BG and thesacrificial member 34 such that the stopper member 14 is formed. Then,the interlayer insulating members 12 and the word lines WL are stackedalternately on the stopper member 14 such that the stacked body 13 isformed. Then, the interlayer insulating member 36, the selection-gateelectrode SG, and the interlayer insulating member 37 are stacked inthis order on the stacked body 13.

Next, as illustrated in FIG. 3, a range in which the memory hole MH isformed using lithography is specified, etching is performed, and therebythe stacked body from the interlayer insulating member 37 to the stoppermember 14 is selectively removed such that the memory hole MH whichpenetrates the stacked body in the Z-direction is formed. Then, thelower end of the memory hole MH reaches the sacrificial member 34 andthe sacrificial member 34 is exposed at the end of the memory hole MH. Apair of memory holes MH are formed on a single sacrificial member 34.Then, the sacrificial member 34 is removed, for example, using wetetching. The removal of the sacrificial member 34 causes the groove 33formed in the back-gate electrode BG to be revealed. The revealed groove33 becomes the junction portion JP. The lower ends of the pair of thememory holes MH are connected to the single common junction portion JP,which forms a single U-shaped cavity.

At this time, the diameter of the memory hole MH is larger at the uppersection unavoidably and is smaller at the lower section. For example,the diameter of the memory hole MH is about 80 nm at the uppermost wordline WL. In addition, the diameter of the memory hole MH is about 50 nmat the lowermost word line WL.

Next, as illustrated in FIG. 4, for example, silicon oxide (SiO₂) with athickness of about 10 nm is deposited on the side surface of the pair ofmemory holes MH and the junction portion JP using a chemical vapordeposition (CVD) method or an atomic layer deposition (ALD) method suchthat the block insulating member 27 is formed. Then, for example,silicon nitride (Si₃N₄) with a thickness of about 7 nm is deposited onthe upper surface of the block insulating member 27 using the samemethod as in the deposition of the block insulating member 27 such thatthe charge storage member 26 is formed. The member thickness of thecharge storage member 26 is set in consideration of the reduction of themember thickness through oxidation to be performed later.

Next, as illustrated in FIG. 5, for example, the surface of the chargestorage member 26 is oxidized using a radical oxidation method such thatsilicon oxide is formed. The formed silicon oxide becomes the tunnelinsulating member 25. The charge storage member 26 remaining withoutbeing subjected to the oxidation has a decreased member thickness. Atthis time, the smaller the diameter of the memory hole MH, the greaterthe member thickness of the formed tunnel insulating member 25. This isbecause, as the diameter becomes smaller, a volume expansion isperformed in a narrower region and the member thickness increases more.

FIG. 6 is a cross-sectional view illustrating the block insulatingmember and the charge storage member before the oxidation in thesemiconductor memory device according to the embodiment when viewed fromthe upper section.

FIG. 7 is a cross-sectional view illustrating the block insulatingmember, the charge storage member after the oxidation, and the tunnelinsulating member in the semiconductor memory device according to theembodiment when viewed from the upper section.

As illustrated in FIG. 6, a distance r indicates a distance from acentral axis P of the memory hole MH to the side surface of the chargestorage member 26 at the time of forming the charge storage member 26.In addition, d_(b) indicates a member thickness of the block insulatingmember 27, d_(e) indicates a member thickness of the charge storagemember 26 before the oxidation, and R indicates a radius of the memoryhole MH.

As illustrated in FIG. 7, d₁ indicates a member thickness of the chargestorage member 26 which is consumed by the oxidation and d₂ indicates amember thickness of the tunnel insulating member 25 formed by theoxidation. Here, when a volume increase rate during conversion of thesilicon nitride member into the silicon oxide member is α, the followingExpression 1 is established with respect to a volume per unit length inthe Z-direction.

α×π×{(r+d ₁)² −r ²}=π×{(r+d ₁)²−(r+d ₁ −d ₂)²}  Expression 1

The left-hand side of the above Expression 1 indicates α times thevolume of the consumed silicon nitride member and the right-hand side ofthe above Expression 1 indicates a volume of the formed silicon oxidemember. The above Expression 1 indicates that α times the volume of theconsumed silicon nitride member and the volume of the formed siliconoxide member are equal. Next, the above Expression 1 is solved withrespect to d₂, which forms the following Expression 2.

d ₂=(r+d ₁)−√{square root over ((r+d ₁)²−α×d₁×(2×r+d ₁))}  Expression 2

Here, the above Expression 2 is described. In order to obtain arelationship between d₂ and the distance r, the above Expression 2 ispartial-differentiated with respect to the distance r, which forms thefollowing Expression 3.

$\begin{matrix}{\frac{\partial d_{2}}{\partial r} = {1 - \frac{r + d_{1} - {\alpha \times d_{1}}}{\sqrt{\left( {r + d_{1}} \right)^{2} - {\alpha \times d_{1} \times \left( {{2 \times r} + d_{1}} \right)}}}}} & {{Expression}\mspace{14mu} 3}\end{matrix}$

Here, when the above Expression 3 satisfies the following Expression 4,the above Expression 3 becomes a decreasing function with respect to thedistance r. That is, the member thickness d₂ of the tunnel insulatingmember 25 formed through the oxidation decreases as the distance rincreases.

$\begin{matrix}{\frac{\partial d_{2}}{\partial r} < 0} & {{Expression}\mspace{14mu} 4}\end{matrix}$

When the condition of the above Expression 4 is applied to the aboveExpression 3, the following Expression 5 is formed.

$\begin{matrix}{{1 - \frac{r + d_{1} - {\alpha \times d_{1}}}{\sqrt{\left( {r + d_{1}} \right)^{2} - {\alpha \times d_{1} \times \left( {{2 \times r} + d_{1}} \right)}}}} < 0} & {{Expression}\mspace{14mu} 5}\end{matrix}$

After the second term on the left-hand side of the above Expression 5 ismoved to the right-hand side, both the sides are squared and reorganizedand then the following Expression 6 is formed.

α×d ₁ ²×(α−1)>0  Expression 6

In order to establish the above Expression 6, the condition of thevolume increase rate α>1 has to be satisfied. That is, in a case of thevolume increase rate α>1, the member thickness d₂ of the tunnelinsulating member 25 which is formed through the oxidation forms adecreasing function with respect to the distance r. According to theembodiment, a material which satisfies the volume increase rate α>1 isused.

When the distance r becomes smaller, the member thickness d₂ of thetunnel insulating member 25 which is formed through the oxidationbecomes greater. This is because the member thickness increases morewhen the charge storage member 26 is subjected to the volume expansionin a narrow region.

In addition, as illustrated in FIG. 6, a relationship of the followingExpression 7 is formed between a radius R of the memory hole MH, thedistance r, the member thickness d_(e) of the charge storage member 26before the oxidation, and the member thickness d_(b) of the blockinsulating member 27.

R=(r+d _(e) +d _(b))  Expression 7

FIG. 8 is a graph illustrating the member thickness of the tunnelinsulating member that is formed through the oxidation, in which thediameter of the memory hole is shown as the abscissa and the memberthickness of the silicon oxide member is shown as the ordinate.

FIG. 9 is a cross-sectional view taken along line IX-IX shown in FIG. 5.

FIG. 10 is a cross-sectional view taken along line X-X shown in FIG. 5.

FIG. 8 is a graph illustrating the member thickness of the formed tunnelinsulating member based on the above Expression 2 and the aboveExpression 7. Here, the member thickness d₁ of the charge storage member26 which is consumed through the oxidation is, for example, about 2 nmand the volume increase rate α is, for example, about 2. The memberthickness d_(b) of the block insulating member 27 is, for example, about10 nm and the member thickness d_(e) of the charge storage member 26before the oxidation is, for example, about 7 nm.

As illustrated in FIG. 8, the smaller the diameter (2×R) of the memoryhole, the greater the member thickness d₂ of the formed tunnelinsulating member 25. This is because the volume expansion is performedin the narrower region and the member thickness increases more as thediameter of the memory hole becomes smaller.

For example, as illustrated in FIG. 9, in a case where the diameter(2×R) of the memory hole MH is about 80 nm and the member thicknessd_(e) of the charge storage member 26 before the oxidation is about 7.0nm, a member thickness of about 4.2 nm from the surface is convertedinto silicon oxide through oxidation. The oxidized member thickness ofabout 4.2 nm becomes the member thickness d₂ of the tunnel insulatingmember 25 and the final member thickness (d_(e)-d₁) of the chargestorage member 26 is about 5 nm which is not oxidized but remains.

In addition, for example, as illustrated in FIG. 10, in a case where thediameter (2×R) of the memory hole MH is about 50 nm and the memberthickness d_(e) of the charge storage member 26 before the oxidation isabout 7.0 nm, an oxidized member thickness is about 4.7 nm. In thiscase, the member thickness is greater than in a case where the diameteris about 80 nm.

For example, in a case where a cross-sectional shape of the memory holeMH is ellipsoidal in an XY plane, the tunnel insulating member 25 isformed in accordance with a curvature radius of the ellipse. The tunnelinsulating member 25 is formed to be thick in a portion where thecurvature radius of the ellipse is small, and the tunnel insulatingmember 25 is formed to be thin in a portion where the curvature radiusis large.

FIGS. 11 to 14 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to theembodiment.

After the tunnel insulating member 25 shown in FIG. 5 is formed, asillustrated in FIG. 11, amorphous silicon (a-Si) with a thickness ofabout 4 nm is deposited on the side surface of the tunnel insulatingmember 25 using a CVD method or an ALD method such that the siliconpillar SP is formed. Then, the inside of the pair of memory holes MH andthe junction portion JP is filled with an insulating material such thatthe insulating member 21 is formed.

Next, as illustrated in FIG. 12, a range in which the slit ST is formedusing lithography is specified, etching is performed with the stoppermember 14 as a stopper, and thereby the stacked body from the interlayerinsulating member 37 to the stacked body 13 is selectively removed suchthat the slit ST which penetrates the stacked body in the Z-directionand extends in the Y-direction is formed. Then, the inside of the slitST is filled with the insulating material such that the insulatingmember 22 is formed.

Next, as illustrated in FIG. 13, after the interlayer insulating member38 is formed on the memory member 15, the silicon pillar SP, theinsulating member 21, the insulating member 22, and the interlayerinsulating member 37, the contact hole 41 is formed by performinglithography and etching. Then, for example, tungsten (W) is deposited onthe inside of the contact hole 41 such that the contact plug CP_(SL) isformed.

Next, as illustrated in FIG. 14, the source line SL that extends in theY-direction is formed on the contact plug CP_(SL) using, for example, aDamascene technique. Then, after the interlayer insulating member 39 isformed on the interlayer insulating member 38 and the source line SL,the contact hole 44 is formed by performing lithography and etching.Then the contact plug CP_(BL) is formed using the same method as themethod for forming the contact plug CP_(SL).

Next, as illustrated in FIG. 1, the bit line BL that extends in theX-direction is formed on the contact plug CP_(BL) using, for example, aDamascene technique.

Radical oxidation is an example of oxidation of the charge storagemember 26; however, the oxidation is not limited to this example. Forexample, thermal oxidation or plasma oxidation may be performed, or acombination of these two types of oxidation may be performed.

Next, an operation of the semiconductor memory device according to theembodiment will be described.

FIG. 15 is a graph illustrating a threshold voltage window of thesemiconductor memory device according to the embodiment, in which thediameter of the memory hole is shown as the abscissa and the thresholdvoltage is shown as the ordinate.

Distributions of the threshold voltage in FIG. 15 show distributions ofthe threshold voltage in a case of four values and the four values areC-level, B-level, A-level, and E-level in descending order of threshold.

Among the threshold voltage distributions in FIG. 15, a distributionshown at the uppermost place shows the threshold voltage distribution ofthe C-level. A distribution shown at the second place from the top showsthe threshold voltage distribution of the B-level. A distribution shownat the third place from the top shows the threshold voltage distributionof the A-level. A distribution shown at the lowermost place shows thethreshold voltage distribution of the E-level.

“Writing characteristics” illustrated in FIG. 15 shows the thresholdvoltage after writing in a case where a predetermined writing voltage isapplied to the word line WL that configures a certain memory cell and avalue of C-level is written. The threshold voltage after writing dependson the diameter (2×R) of the memory hole MH. The larger the diameter ofthe memory hole MH, the lower the likelihood of the electric field beingconcentrated and the lower the threshold voltage after writing.Therefore, as the lower limit value of the C-level in the thresholdvoltage distribution, a threshold voltage CV required when the diameterof the memory hole MH is the maximum value Rmax has to be assumed. Inaddition, the threshold voltage corresponding to the B-level needs to beset in a range lower than the threshold voltage CV.

“Read voltage Vread” shown in FIG. 15 is a voltage that is applied toanother memory cell configured of the same silicon pillar SP as thememory cell which is a read target such that the memory cell is in an ONstate regardless of a value that is written in. Thus, the read voltageVread needs to be set to be much higher than the C-level which is thehighest threshold voltage level. A difference between the read voltageVread and the threshold voltage CV is “overdrive Vod”.

In addition, “read disturb characteristics” show an amount of change ofthe threshold voltage due to a tunneling current unavoidably flowing inthe memory cell when a predetermined read voltage Vread has been appliedto the memory cell of E-level. The greater the difference between theread voltage Vread and the original threshold voltage written in to thememory cell, the more the amount of threshold voltage change due to theread disturb. An amount of the threshold voltage change of the memorycell of the E-level in a state of being removed is greatest. Inaddition, the read disturb characteristics depends on the diameter ofthe memory hole MH, and thus the smaller the diameter of the memory holeMH, the greater the amount of the change of the threshold level in orderfor the electric field to be concentrated. Therefore, as the upper limitvalue of the E-level in the threshold voltage distribution, a thresholdvoltage EV required when the diameter of the memory hole MH is theminimum value Rmin has to be assumed. In addition, the threshold voltagecorresponding to the A-level needs to be set in a range higher than thethreshold voltage EV.

As illustrated in FIG. 1, in the semiconductor memory device 1 accordingto the embodiment, the diameter of the memory hole MH changes dependingon a position in the Z-direction and, for example, the lower theposition, the smaller the diameter. As illustrated in FIG. 15, in a casewhere the diameter of the memory hole MH in a single memory cell ormemory cell string changes in a range from the minimum value Rmin to themaximum value Rmax, a reliable predetermined value is written regardlessof the size of the diameter of the memory hole MH and in order to read,there is a need to set the threshold voltage of the A-level and thethreshold voltage of the B-level to be within a range of the “thresholdvoltage window W” which is greater than the value EV and less than thevalue CV. The greater the range of the change (Rmax-Rmin) of thediameter of the memory hole MH, the narrower the threshold window W, andthe smaller a margin of the threshold voltage between levels, whichcauses the operation of the semiconductor memory device 1 to bedifficult.

According to the embodiment, the smaller the diameter of the memory holeMH, the thicker the tunnel insulating member 25. Thus, the electricfield is likely to be concentrated on the tunnel insulating member 25 ofthe memory cell. However, when the tunnel insulating member 25 is thick,the effect of preventing the tunneling current from flowing isexcellent. Therefore, it is possible to decrease the threshold voltageof the E-level when the diameter of the memory hole MH is the minimumvalue Rmin. That is, the member thickness of the tunnel insulatingmember 25 becomes greater, which prevents the read disturb fromoccurring. Then, it is possible to decrease the threshold voltage EV. Asa result, the threshold window W is widened and it is possible tostabilize driving of the semiconductor memory device 1.

Next, an effect of the embodiment will be described.

In the semiconductor memory device according to the embodiment, it ispossible to widen the threshold window W by (a) and (b) shown in thefollowing description.

(a) The larger the diameter (2×R) of the memory hole MH, the thinner thetunnel insulating member 25.

According to (a), if the same cell current is obtained, it is possibleto decrease the overdrive Vod to an equivalent amount obtained as theelectrical member thickness (EOT) of the tunnel insulating member 25becomes thinner. The decrease of the overdrive Vod brings about decreaseof the read voltage Vread. Thus, the read disturb is unlikely to occurand it is possible to decrease the threshold voltage EV.

(b) The smaller the diameter (2×R) of the memory hole MH, the thickerthe tunnel insulating member 25.

According to (b), the tunneling current, particularly a direct tunnelingcurrent is unlikely to flow. Therefore, the read disturb is unlikely tooccur and it is possible to decrease the threshold voltage EV.

According to (a) and (b), since it is possible to decrease the thresholdvoltage EV, it is possible to widen the threshold window W.

Table 1 shows experimental examples of the threshold voltage window ofthe semiconductor memory device according to the embodiment. The memberthickness of the tunnel insulating member is represented by T.

Example 1 in Table 1 shows an example of a case where the diameter ofthe memory hole MH in the upper section is 80 nm, the member thicknessof the tunnel insulating member 25 is 4.2 nm, the diameter in the lowersection is 50 nm, and the member thickness is 4.7 nm. At this time, thethreshold voltage CV, overdrive Vod, the read voltage Vread, thethreshold voltage EV, and the threshold window W are 4.00 V, 2.72 V,7.32 V, 1.32 V, and 2.68 V, respectively.

Comparative Example 1 in Table 1 shows an example of a case where thediameter of the memory hole MH in the upper section is 80 nm, thediameter in the lower section is 50 nm, and the member thickness of thetunnel insulating member 25 is 4.2 nm without change. At this time, thethreshold voltage CV, overdrive Vod, the read voltage Vread, thethreshold voltage EV, and the threshold window W are 4.00 V, 2.72 V,7.32 V, 2.00 V, and 2.00 V, respectively.

Comparative Example 2 in Table 1 shows an example of a case where thediameter of the memory hole MH in the upper section is 80 nm, thediameter in the lower section is 50 nm, and the member thickness of thetunnel insulating member 25 is 4.7 nm without change. At this time, thethreshold voltage CV, overdrive Vod, the read voltage Vread, thethreshold voltage EV, and the threshold window W are 4.00 V, 2.77 V,7.37 V, 1.37 V, and 2.63 V, respectively.

TABLE 1 Experimental 2XR T CV Vod Vread EV W example (nm) (nm) (V) (V)(V) (V) (V) Example 1 80 4.2 4.00 2.72 7.32 1.32 2.68 50 4.7 Comparative80 4.2 4.00 2.72 7.32 2.00 2.00 example 1 50 Comparative 80 4.7 4.002.77 7.37 1.37 2.63 example 2 50

As shown in Table 1 above, the semiconductor memory device according toExample 1 includes the tunnel insulating member which has the greatermember thickness T at a portion where the memory hole MH has the minimumdiameter of 50.0 nm, as compared to the semiconductor memory deviceaccording to Comparative Example 1. In addition, the semiconductormemory device according to Example 1 includes the tunnel insulatingmember which has the smaller member thickness T at a portion where thememory hole MH has the maximum diameter of 80.0 nm, as compared to thesemiconductor memory device according to Comparative Example 2.

Thus, the overdrive Vod is decreased to 2.72 V and then it is possibleto decrease the Read voltage Vread to 7.32 V. The Read voltage Vread isdecreased to 7.32 V, and thereby the threshold voltage EV is decreasedto 1.32 V, and then, it is possible to widen the threshold window W to2.68 V.

In the semiconductor memory device according to the embodiment, thelarger the diameter of the memory hole MH, the smaller the memberthickness of the tunnel insulating member, and the smaller the diameterof the memory hole MH, and the greater the member thickness of thetunnel insulating member. As a result, it is possible to provide thesemiconductor memory device that includes a wide threshold window and amethod for manufacturing the semiconductor memory device.

In addition, the member thickness of the tunnel insulating member 25 isautomatically controlled by the diameter of the memory hole MH. In otherwords, the member thickness of the tunnel insulating member 25 which isself-aligning is determined. Therefore, the thickness of the tunnelinsulating member 25 does not depend on the shape of the memory hole MH.For example, the embodiment may be applied to a bowed shape in which thememory hole MH has the maximum diameter at an intermediate layer of wordlines WL of a single memory string and the member thickness of thetunnel insulating member 25 is determined according to the diameter ofthe memory hole MH.

Further, the embodiment may be applied to a case where the shape of thememory hole MH is ellipsoidal in a single layer of word lines WL and thetunnel insulating member 25 is formed according to the curvature radius.That is, since the smaller the curvature radius the thicker the tunnelinsulating member 25 is formed to be, as a result, the central portionof the memory hole MH is formed to be closer to a circle. Normally, thesmaller the curvature radius, the more the read disturb is likely tooccur. Since the variation of the curvature radius in the memory hole MHaccording to the embodiment is decreased, it is possible to prevent theread disturb.

A magnitude relation of a diameter of the memory hole MH in an XZ planecan be confirmed as a magnitude relation of a width of the memory holeMH in the X direction.

Second Embodiment

Next, the second embodiment will be described.

FIG. 16 is a cross-sectional view illustrating the semiconductor memorydevice according to the embodiment.

FIG. 17 is a cross-sectional view taken along line XVII-XVII shown inFIG. 16.

FIG. 18 is a cross-sectional view taken along line XVIII-XVIII shown inFIG. 16.

First, a configuration of the semiconductor memory device according tothe embodiment is described.

As illustrated in FIG. 16, the tunnel insulating member 25 of thesemiconductor memory device 1 according to the embodiment is formed ofan oxide-nitride-oxide (ONO) member which includes a top-oxide member51, a middle-nitride member 52, and a bottom-oxide member 53.

As illustrated in FIGS. 17 and 18, the larger the diameter (2×R) of thememory hole MH, the thinner the bottom-oxide member 53, and the smallerthe diameter of the memory hole MH the thicker the bottom-oxide member53.

For example, in FIG. 17, the thickness of the tunnel insulating member25 formed of the ONO member is formed as follows. The diameter (2×R) ofthe memory hole MH is about 78 nm, the thickness of the block insulatingmember 27 is about 10 nm, the thickness of the charge storage member 26is about 5.0 nm, the thickness of the top-oxide member 51 of the tunnelinsulating member 25 is about 3.0 nm, the thickness of themiddle-nitride member 52 is about 2.2 nm, the thickness of thebottom-oxide member 53 is about 1.6 nm, and the thickness of the siliconpillar SP is about 3.0 nm.

In FIG. 18, the thickness of the tunnel insulating member 25 formed ofthe ONO member is as follows. In a case where the diameter (2×R) of thememory hole MH is about 52 nm, the thickness of the bottom-oxide member53 is about 1.8 nm. The member thicknesses other than the bottom-oxidemember 53 are the same as those in FIG. 17.

Configurations according to the embodiment which are not described aboveare the same as those of the first embodiment.

Next, the method for manufacturing the semiconductor memory deviceaccording to the embodiment will be described.

FIGS. 19 and 20 are cross-sectional views illustrating the method formanufacturing the semiconductor memory device according to theembodiment.

First, the method is the same as that according to the first embodimentuntil the charge storage member 26 is formed inside the memory hole MH.

Next, as illustrated in FIG. 19, for example, the silicon oxide isdeposited on the side surface of the charge storage member 26 of whichthe thickness is 5.0 nm using a CVD method or an ALD method such thatthe top-oxide member 51 of which the thickness is 3.0 nm is formed.Then, the silicon nitride is deposited on the side surface of thetop-oxide member 51 using the same method as that in forming thetop-oxide member 51 such that about 3.0 nm of the middle-nitride member52 is formed.

Next, as illustrated in FIG. 20, for example, the surface of themiddle-nitride member 52 is oxidized using a radical oxidation methodsuch that the bottom-oxide member 53 is formed.

At this time, for example, in the uppermost word line WL, themiddle-nitride member 52 is oxidized to a depth of about 0.8 nm from thesurface and the bottom-oxide member 53 of which the thickness is about1.6 nm is formed. The final member thickness of the middle-nitridemember 52 is about 2.2 nm. In addition, in the lowermost word line WL,the middle-nitride member 52 is oxidized to a depth of about 0.8 nm fromthe surface and the bottom-oxide member 53 of which the thickness isabout 1.8 nm is formed. That is, the smaller the diameter (2×R) of thememory hole MH, the thicker the bottom-oxide member 53. The final memberthickness of the middle-nitride member 52 is about 2.2 nm in the lowestword line WL. In this way, the tunnel insulating member 25 is formed toinclude the top-oxide member 51, the middle-nitride member 52, and thebottom-oxide member 53.

The other manufacturing methods, operations, and effects according tothe embodiment are the same as in the first embodiment described above.

Third Embodiment

Next, the third embodiment will be described.

FIG. 21 is a cross-sectional view illustrating the semiconductor memorydevice according to the embodiment.

FIG. 22 is a cross-sectional view taken along line XXII-XXII shown inFIG. 21.

FIG. 23 is a cross-sectional view taken along line XXIII-XXIII shown inFIG. 21.

First, a configuration of the semiconductor memory device according tothe embodiment is described.

As illustrated in FIGS. 22 and 23, the semiconductor memory device 1according to the embodiment is different compared to the secondembodiment in that the thickness of the top-oxide member 51 becomesgreater as the diameter (2×R) of the memory hole MH becomes smaller.

For example, in FIG. 22, the thickness of the tunnel insulating member25 is as follows. The diameter (2×R) of the memory hole MH is about 78nm, the thickness of the block insulating member 27 is about 10 nm, thethickness of the charge storage member 26 is about 5.0 nm, the thicknessof the top-oxide member 51 of the tunnel insulating member 25 is about3.1 nm, the thickness of the middle-nitride member 52 is about 2.2 nm,the thickness of the bottom-oxide member 53 is about 1.6 nm, and thethickness of the silicon pillar SP is about 3.0 nm.

In addition, In FIG. 23, the thickness of the tunnel insulating member25 is as follows. In a case where the diameter (2×R) of the memory holeMH is about 52 nm, the thickness of the top-oxide member 51 is about 3.3nm and the thickness of the bottom-oxide member 53 is about 1.8 nm. Themember thicknesses other than the top-oxide member 51 and thebottom-oxide member 53 are the same as those in FIG. 22.

In a case where the diameter of the memory hole MH is about 78 nm, thethickness of the top-oxide member 51 is about 3.1 nm. Meanwhile, in acase where the diameter of the memory hole MH is about 52 nm, thethickness of the top-oxide member 51 is about 3.3 nm, and thus thethickness is greater, compared to the case where the diameter of thememory hole MH is about 78 nm. In addition, in a case where the diameterof the memory hole MH is about 78 nm, the thickness of the bottom-oxidemember 53 is about 1.6 nm. Meanwhile, in a case where the diameter ofthe memory hole MH is about 52 nm, the thickness of the bottom-oxidemember 53 is about 1.8 nm, and thus the thickness is greater, comparedto the case where the diameter of the memory hole MH is about 78 nm

Configurations according to the embodiment which are not described aboveare the same as those of the second embodiment described above.

Next, the method for manufacturing the semiconductor memory deviceaccording to the embodiment will be described.

First, the method is the same as that according to the second embodimentuntil the charge storage member 26 is formed inside the memory hole MH.Then, using the same method as the method for forming the tunnelinsulating member 25 according to the first embodiment, for example, thecharge storage member 26 is oxidized using a radical oxidation methodand then the formed silicon oxide becomes the top-oxide member 51.

The other manufacturing methods according to the embodiment are the sameas in the second embodiment.

Next, effects of the semiconductor memory device according to theembodiment will be described.

In the semiconductor memory device according to the embodiment, thelarger the diameter of the memory hole MH, the smaller the memberthickness of the top-oxide member 51 as well as the bottom-oxide member53, and the smaller the diameter of the memory hole MH, the greater themember thickness of the top-oxide member 51 as well as the bottom-oxidemember 53. Therefore, it is possible to further widen the thresholdwindow W.

The other operations and effects according to the embodiment are thesame as in the second embodiment described above.

According to the first embodiment to the third embodiment which aredescribed above, the middle-nitride member 52 may not be a perfectnitride member, but may be a silicon oxynitride member containingoxygen.

In addition, an example of the diameter of the memory hole MH isdescribed, in which the diameter is larger in the upper section and thelower the section, the smaller the diameter; however, the configurationis not limited thereto. For example, a bowing phenomenon is caused tooccur during the formation of the memory hole MH and the memory hole MHmay have a bowed shape in which the memory hole MH has the greatestdiameter in the middle.

Further, the configuration in which the silicon pillar SP is U-shaped isdescribed; however, the silicon pillar SP may be a straight type inwhich the source line is disposed on the lower section.

Further, an example of the method for manufacturing the semiconductormemory device is described, in which, after the interlayer insulatingmembers 12 and the word lines WL are stacked alternately, the memoryhole MH is formed, and then the memory member 15 and the silicon pillarSP are formed; however, the method is not limited thereto. For example,the stacked body may be formed by the following processes. Theinterlayer insulating members 12 and the sacrificial members are stackedalternately such that the stacked body is formed. The memory hole MH isformed inside the stacked body. After the charge storage member isformed in the memory hole MH, the tunnel insulating member is formedthrough the same processes according to the first to third embodimentsdescribed above. A groove that extends in the Z-direction in the stackedbody is formed and then the sacrificial member is removed through thegroove. The block insulating member and the electrode member aredeposited in this order at the position from which the sacrificialmember is removed. It is possible to achieve the same effects as in theembodiments even when the semiconductor memory device is formed usingthese processes.

According to the embodiments described above, the larger the diameter ofthe memory hole, the smaller the member thickness of the tunnelinsulating member. In addition, the smaller the diameter of the memoryhole, the greater the member thickness of the tunnel insulating member.As a result, it is possible to provide a semiconductor memory devicethat includes a wide threshold window, and the method for manufacturingthe semiconductor memory device.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A method for manufacturing a semiconductor memorydevice comprising: forming a first electrode member on a flat surfaceperpendicular to a first direction, forming a second electrode memberparallel to the first electrode member, the second electrode memberbeing disposed above the first electrode member, forming a memory holethat penetrates the first electrode member and the second electrodemember in the first direction from above, a diameter of the memory holeat a position of the first electrode member being made smaller than adiameter of the memory hole at a position of the second electrodemember, forming a first charge storage portion on a side surface of thefirst electrode member via an insulating material and a second chargestorage portion on a side surface of the second electrode member via theinsulating material, forming a first insulating member and a secondinsulating member by oxidizing the first charge storage portion and thesecond charge storage portion, a thickness of first charge storageportion being made smaller than a thickness of the second charge storageportion after the oxidation, and forming a semiconductor layer at aninner side of the first insulating member and the second insulatingmember.
 2. The method according to claim 1, wherein the oxidationincludes radical oxidation, thermal oxidation, or plasma oxidation. 3.The method according to claim 1, wherein the first insulating member andthe second insulating member contain silicon oxide.
 4. The methodaccording to claim 1, wherein the first insulating member and the secondinsulating member contain silicon oxynitride.
 5. The method according toclaim 1, wherein a thickness of the first insulating member is largerthan a thickness of the second insulating member.
 6. The methodaccording to claim 1, further comprising: forming a third insulatingmember on a side surface of the first insulating member and the secondinsulating member.
 7. The method according to claim 6, wherein the thirdinsulating member contains silicon oxide.
 8. The method according toclaim 7, further comprising: forming a fourth insulating member on aside surface of the first insulating member and the second insulatingmember before the forming the third insulating member.